1. Field of the Invention
The present invention relates to an image forming apparatus which forms images on sheets, a sheet processing apparatus which performs various kinds of post-processing such as folding and book-binding on sheets with images formed thereon, and an image forming system including the image forming apparatus and the sheet processing apparatus.
2. Description of the Related Art
FIG. 23A is a view showing an example of a cover for a conventional image forming apparatus. In FIG. 23A, a cover 351 covers all of the following: a conveying path via which an image is formed on a sheet fed from any of cassettes provided in the apparatus, a conveying path via which a sheet with an image formed thereon is discharged from the apparatus, and a conveying path via which a sheet with an image formed on one side thereof is inverted and conveyed to an image forming unit in a double-sided recording mode. Therefore, when the cover 351 is opened, it is possible to access all the conveying paths.
The above described cover provided in the image forming apparatus is not opened during normal image formation, but is opened while image formation is not carried out, e.g. during a jam removal process or maintenance. Thus, when the cover is opened during image formation, it is judged that an abnormal state has occurred, and then all the operations being performed are stopped, which is unproductive.
To address this problem, Japanese Laid-Open Patent Publication (Kokai) No. H08-082960 has proposed an image forming apparatus which is provided with an open/close cover for removing recording sheets remaining in a double-sided recording unit as shown in FIG. 23B, so that one-sided recording can be performed even if the open/close cover is opened insofar as a double-sided recording mode is not set.
In a conventional image forming system including the image forming apparatus as described above, one-sided recording can be performed without stopping the operation of the entire system when the jam removal process is carried out in the double-sided recording unit, but when the cover is opened/closed for maintenance of a sheet processing apparatus (such as a folding unit, a book-binding unit, or a finisher), the operation of the entire system has to be stopped, which is unproductive.
Further, post-processes such as a bundle-discharging process, stapling process, folding process, and book-binding process desired by the user can be realized in one image forming system by connecting a plurality of sheet processing apparatuses intended exclusively for the respective post-processes to the image forming apparatus, but to carry out maintenance on the sheet processing apparatuses without stopping the operation of the entire system, the sheet processing apparatuses to be subjected to maintenance has to be detached from the system to which the plurality of sheet processing apparatuses are connected, and then moved. On this occasion, the image forming system must be initialized again so as to recognize a sheet processing apparatus to which is connected a controller which controls the overall operation of the system.
Further, it is necessary to regularly carry out maintenance on the sheet processing apparatus by e.g. replacement of parts, adjustments, and cleaning after a predetermined number of sheets are passed through the sheet processing apparatus, but all the sheets are not necessarily passed through the same conveying path. In a stapling mode, folding mode, book-binding mode, etc. of the sheet processing unit, the number of sheets passed through conveying paths varies according to settings made by the user, and the timing for maintenance is different depending on the sheet processing apparatuses and the conveying paths in the image forming system. For example, in the case of replacement of parts for maintenance, the number of sheets which can be endured by parts differs even if the number of sheets passed through the parts is the same, and hence the timing for maintenance is different depending on the sheet processing apparatuses and the conveying paths in the system.